Evaluating IBA and NAA for improved rooting in pot mum cultivation (Dendranthema grandiflora Tzvelev.)

Introduction

Chrysanthemum (Dendranthema grandiflora Tzvelev.), often called "pot mum" or "garden mum," is one of the most admired flowering plants grown across the world. Its wide range of vibrant colors, attractive flower shapes and long-lasting blooms make it a favorite among gardeners, florists and flower lovers alike. Belonging to the family Asteraceae, chrysanthemums have been cherished for centuries for their ornamental value and are now an essential part of the global floriculture trade (Roopa et al., 2018; Teale et al., 2006) [16,22] . Whether used as potted plants for homes and offices or as cut flowers in bouquets and decorations, chrysanthemums continue to hold a special place in both local and international markets. In commercial cultivation, maintaining the true qualities of the desired variety such as color, shape and blooming time is extremely important (Sevik and Guney, 2013) [18] . Since growing chrysanthemums from seeds often results in plants with mixed traits, growers mostly depend on vegetative propagation using terminal cuttings. This method ensures that every new plant is genetically identical to the parent plant, preserving its uniform appearance and quality (Waseem et al., 2011) [24] . However, one of the main challenges in this propagation process is rooting. The success of chrysanthemum cultivation largely depends on how quickly and strongly the cuttings develop roots. Healthy roots help in better absorption of nutrients and water, leading to stronger growth, healthier foliage and more uniform flowering (Guney et al., 2021) [5] . Unfortunately, natural root formation can sometimes be slow or uneven, which affects overall plant establishment and productivity. To overcome this, growers often use plant growth regulators, particularly a group of hormones known as auxins. Auxins naturally occur in plants and control several key growth processes such as cell division, elongation and differentiation. They play a crucial role in stimulating root initiation, especially in vegetative cuttings (Akhtar et al., 2015) [2] . By applying synthetic auxins externally, growers can encourage faster and more uniform root development. This practice has become an essential part of modern propagation techniques in ornamental horticulture. Among synthetic auxins, Indole-3-butyric acid (IBA) and α-Naphthalene acetic acid (NAA) are the two most widely used for promoting root formation in cuttings. IBA is highly preferred because it is stable, effective, and compatible with a wide range of plant species (Kentelky et al., 2021) [9] . It promotes the formation of strong and well-developed roots without causing much damage or toxicity. On the other hand, NAA is particularly effective in inducing early root initiation and can increase the number of roots per cutting (Lee et al., 2024) [11] . However, at higher concentrations, NAA may lead to callus formation or slow root elongation, which can negatively affect plant growth (Debasis et al., 2000) [3] . Therefore, finding the right type and concentration of auxin is crucial to achieving the best rooting results. In pot mum cultivation, quick and uniform rooting is especially valuable because it saves time during propagation, reduces the risk of transplant shock and ensures more even plant growth later in the season (Suvija et al., 2016) [21] . When cuttings root faster and grow more uniformly, growers can produce highquality plants more efficiently, meeting the market's demand for attractive and healthy ornamentals. For both small nurseries and large-scale commercial farms, improving the rooting process directly translates to better productivity and profitability (Sahoo et al., 2025) [17] . Moreover, using optimal hormone treatments can make the entire propagation system more sustainable by reducing losses and improving resource efficiency. This study focuses on evaluating the effects of different concentrations of IBA and NAA on the rooting performance of chrysanthemum cuttings. It aims to determine which hormone and concentration combination gives the best results in terms of rooting percentage, number of roots per cutting, root length and overall plant growth.

Materials and Methods

The Experiment was conducted during November of the year 2023 at the College of Horticulture, Bengaluru to study the effect of IBA and NAA on the rooting of chrysanthemum cuttings at the research polyhouse, Department of Floriculture and Landscape Architecture. The terminal stem cuttings of uniform length (5-7 cm) having one or two buds were excised from the mother plants maintained under artificial lighting. Six auxin formulations were used with different concentrations, with twenty-five cuttings in each treatment and replicated three times. Thereafter, the cut ends were dipped (2-3 min) in rooting hormone solution of IBA (300, 400, 500 ppm) and NAA (150, 200, 250 ppm) individually, initially dissolved in 70% ethanol and made to a volume of 1000 ml with distilled water. The basal part of the cuttings of the control was treated with distilled water. The treated cuttings were planted in the protrays filled uniformly with cocopeat. The trays were placed under a polytunnel provided with sprinklers to maintain optimum moisture and relative humidity (85%) for rooting. The planted cuttings were allowed to root for 30 days. The cuttings were carefully removed from the trays and washed to eliminate any media particles clinging to the roots. Observations related to root and shoot characteristics were recorded, including the number of days taken for root initiation, rooting percentage, root length, number of roots per cutting, shoot length and internodal length. The experiment followed was Factorial Completely Randomised Design (FCRD) with seven treatments and five varieties replicated thrice and statistically analysed.

Results and Discussion

Days taken for root initiation

Minimum days taken for root initiation (8.57 days) was recorded in cuttings treated with IBA@400 ppm (T 3 ) which was on par with NAA@200 ppm (T 6 ) (8.56 days) and it was maximum in cuttings treated with Distilled water (T 1 ) (14.25 days). Among the varieties early rooting was observed in var. Camargo (V 5 ) (9.42 days) followed by var. Mount Ventox (V 3 ) (10.21 days). Delayed rooting was recorded in the variety Zizinho Yellow (V 1 ) (10.34 days). Interaction between the rooting hormone and varieties illustrated that early rooting was recorded in T 3 V 5 (7.33 days) which was on par with T 6 V 5 (7.93 days). Delayed root initiation was observed in T 1 V 2 (15.53 days) (Table 1). Early rooting was driven by endogenous auxin translocation, while exogenous IBA boosted cell proliferation and elongation (Yusnita et al., 2017; Ranjbar and Ahmadi, 2016) [25,15] . Exogenous auxins like IBA and NAA reduced rooting time and enhanced root count compared to controls (Kamal et al., 2024) [8] .

Number of roots

The maximum number of roots per cutting was observed in cuttings treated with IBA@400 ppm (T 3 ) (42.53) followed by cuttings treated with NAA@200 ppm (T 6 ) (41.45) (figure 1). However, the minimum number of roots was recorded in cuttings treated with distilled water (T 1 ) (20.62). Among varieties the highest number of roots were found in var. Camargo (V 5 ) (38.58) while the lowest was found in var. Flavio (V 4 ) (28.67). Interaction between the rooting hormone and variety illustrated that the maximum number of roots (49.67) was found in T 3 V 5 which was on par with T 6 V 5 (49.40). Whereas, the minimum number of roots per plant was observed in T 1 V 4 (15.53) (Table 1). Auxins like IBA and NAA are crucial for the initiation of adventitious root (AR) primordia, as root cell division relies on these hormones. The effectiveness of different auxin concentrations varies by species. Optimal auxin levels promoted rooting by facilitating the synthesis of IBA conjugates, which were beneficial for difficult-to-root plants Radhari et al., 2014 [13] . Joel et al. (2023) [7] reported that the application of optimal concentrations of IBA significantly enhanced the formation of adventitious roots by promoting cell division and elongation at the basal end of the chrysanthemum cuttings.

Root length

The maximum root length of (4.71cm) was recorded in cuttings treated with NAA@250 ppm (T 7 ) followed by IBA@400 ppm (T 3 ) (4.4 cm) and NAA@200 ppm (T 6 ) (4.29 cm) in figure 1. However, the minimum root length was found in cuttings treated with distilled water (T 1 ) (2.74 cm) (Table 1). Among the varieties the maximum root length was recorded in var. Camargo (V 5 ) (4.58 cm) and the minimum length of roots was observed in the var. Zizinho Yellow (V 1 ) (3.62 cm). Interaction between the rooting hormone and varieties revealed that increased root length (4.98 cm) was recorded in T 7 V 5 followed by T 3 V 5 (4.85 cm). Decreased root length was recorded in T 1 V 1 (1.81 cm). The significant increase in root length is likely due to auxins enhancing carbohydrate hydrolysis, metabolite accumulation, protein synthesis, cell enlargement, and division (Strydem and Hartman, 1960; Janakiram et al., 2006) [19,6] . Exogenous synthetic auxins can boost endogenous auxin effects or directly induce root formation (Kralik and Sebahenek, 1980) [10] .

Rooting percentage

The maximum rooting percentage was recorded in cuttings treated with IBA@400 ppm (T 3 ) (96.47%) which was on par with NAA@200 ppm (T 6 ) (96.40%). Minimum per cent rooting was registered in terminal cuttings treated with distilled water (T 1 ) (76.93%). Among the varieties, the maximum rooting percentage was observed in var. Zizinho Yellow (V 1 ) (90.09%) which was on par with var. Mount Kenya (V 2 ) (89.76%). However, the rooting percentage was found to be minimal in the var. Mount Ventox (V 3 ) (88.28%). The interaction between the rooting hormone and the varieties illustrated that the highest rooting percentage was recorded in T 3 V 4 (98.10%), which was on par with T 6 V 5 (98%) and T 6 V 1 (97.60%). It was lowest (74.67%) in T 1 V 3 (Table 2). Cuttings treated with IBA at 400 ppm significantly improved rooting. This could be because auxins like IBA and NAA enhance adventitious root formation and regulate root growth, including lateral root development and gravity responses, through auxin transport. In support of these statement, enhanced rooting was reported by Joel et al. (2023) [7] in chrysanthemum and (Ghofrani et al., 2013; Prince and Beniwal, 2017) [4,12] in carnation.

Shoot length

The maximum shoot length was recorded in cuttings treated with NAA@250 ppm (T 7 ) (7.65 cm) which was on par with IBA@400 ppm (T 3 ) (7.62 cm) and it was found to be the minimum in cuttings treated with distilled water (T 1 ) (5.35 cm).

Among the varieties the maximum shoot length was recorded in var. Mount Ventox (V 3 ) (7.61 cm), and the minimum length of the shoot was observed in the var. Camargo (V 5 ) (6.57 cm). Interaction between the rooting hormone and varieties illustrated that increased shoot length (8.72 cm) was observed in T 7 V 3 and it was on par with T 3 V 3 (8.16 cm). The shoot length was decreased in T 1 V 5 (4.24 cm) (Table 2). An increase in shoot length was observed following the application of auxin-based rooting hormones such as NAA and IBA. The use of these hormones at optimal concentrations (IBA @ 400 ppm and NAA @ 250 ppm) resulted in the longest shoots, enhancing the quality of rooted cuttings, improving their export potential, facilitating easier transplanting and promoting better field establishment after transplantation (Susaj et al., 2012) [20] . These findings are in accordance with those of Abrol et al. (2018) [1] in chrysanthemum and Ullah et al. (2013) [23] in marigold, who also reported significant improvement in shoot growth and overall plant vigor following auxin treatments.

Internodal length

The perusal data on internodal length is found to be nonsignificant among the varieties treated with different rooting hormones. Though the maximum internodal length was observed in var. Mount Ventox (V 3 ) (2.05 cm) and it was found to be the minimum in var. Camargo (V 5 ) (1.53 cm). Among the rooting hormones the maximum internodal length was recorded in cuttings treated with NAA@250 ppm (T 7 ) (2.22 cm). Interaction between rooting hormones and varieties revealed that the maximum internodal length of (2.48 cm) was observed in T 7 V 4 . It was found to be a minimum (0.91 cm) in T 1 V 5 (Table 2).

Conclusion

The study demonstrated that exogenous application of IBA@400 ppm and NAA@200 ppm significantly enhanced rooting performance in chrysanthemum cuttings. These treatments induced early root initiation, higher root number, greater root length and superior rooting percentage compared to the control. Among the varieties tested, Camargo exhibited the best rooting response, highlighting genotypic influence. The findings suggested that adopting optimum concentrations of IBA or NAA can improve propagation efficiency, uniformity and establishment of pot mums under polyhouse conditions.

Acknowledgement

I would like to express my gratitude to the Department of Floriculture and Landscaping, College of Horticulture, Bengaluru, for providing research facilities and guidance during the study. Special thanks are extended to faculty members and staff for their technical support throughout the investigation.

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